Question: What was the royal of the noble rank of the head of state in the Roman Empire?
Paraphrase: What was the illustrious of the respectable rank of the head of state within the Roman Empire?
SPARQL (Wikidata):  select distinct ?obj where { wd:Q2277 wdt:P1906 ?obj . ?obj wdt:P31 wd:Q355567 } 
Answer: Roman emperor